1. Field of the Invention
The present invention relates to a drive wave generation circuit which generates a drive wave for driving a piezo actuator.
2. Description of the Related Arts
Piezo actuators using elongation and contraction of a piezo element have been proposed and are attracting attention as promising ultra-small actuators (KONICA MINOLTA TECHNOLOGY REPORT VOL. 1 (2004), p. 23-26). Such piezo actuators are employed in a mechanism for driving an image capturing element in small cameras, such as those provided in cellphones, to compensate for camera shake or in a focusing mechanism that moves a lens.
In a piezo actuator, a voltage is applied to a piezo element (piezoelectric element) to elongate and contract the element, thereby generating a reciprocating movement of a drive shaft. By moving the drive shaft in one direction at one speed and in the opposite direction at a different speed (i.e., by causing slow elongation and quick contraction, or vice versa), a movable object in frictional contact with the drive shaft can be moved. Because elongation and contraction of a piezo element is used as a driving force in this way, linear movement of an object can be achieved without coils or the like, making it possible to downsize actuators.
In order to change the speed of reciprocating movement of the drive shaft, the waveform of a voltage applied to the piezo element must be changed. For example, in order to cause slow elongation and quick contraction, a voltage in a first direction must be applied slowly and a voltage in the other opposite direction applied abruptly.
To make duty ratio and timing variable for the voltage application pattern described above, setting data may be written in registers. For example, data transferred through a serial bus such as an I2C bus may be set in a register. “0” is set in the register during initialization after power on. When the data is “0”, a drive wave is not generated. Accordingly, no drive wave is output until predetermined data is set in the register through the serial bus and thus operation for the initialization takes a long time.
In the case of focusing of a camera, typically the direction of infinity is set as the initial position. Therefore, a predetermined number of driving waves for driving the lens in a predetermine direction may be output during initialization. However, in operation, one may sometimes want to move the lens in the direction of macro as an initial setting.